A plasma is a gaseous collection of ions, neutral atoms or molecules, and free electrons. Plasmas are electrically conductive because the unbound charged particles couple easily to electromagnetic fields. While the definition of the term “plasma” can vary, it usually includes some element of “collective” behavior, meaning that any one charged particle can interact with a large number of other charged particles in the plasma.
Plasma can be used as a light source in mass spectrometry applications, For example, a microplasma photoionization (MPPI) source can be used in mass spectrometers to provide ultraviolet (UV) light to (photo) ionize analyte molecules. Photoionization can be achieved using plasma-based lamps in which light is produced as a result of the excitation of rare gas atoms. The emitted UV light can be at a variety of wavelengths based on the gas composition.
There is a need to increase the power of the emitted radiation from plasma UV sources. A saturation limit is often reached using a single RF/microwave plasma source; increasing the RF power realizes a diminished return in output UV radiation power. While it is possible to provide RF/microwave power to multiple plasma generation devices to provide increased UV output, other drawbacks make this option unattractive. For example, multiple sources and multiple feeds are required, resulting in a more complex and comparatively expensive UV source, Moreover, the resonance frequency of each component is not necessarily tuned to the frequency of the input RF/microwave power source. Because each component may have a different resonance frequency, each component will require its own designated RF/microwave power source, and multiple connections will be required. This would result in a more complex structure to realize a more powerful UV output from the MPPI. This complexity adds to the cost and size of the MPPI.
What is needed, therefore, is a plasma generation device that overcomes at least the deficiencies and drawbacks of the known UV light sources described above.